How to ensure animated clones get lost in the crowd

By Colin Barras No epic movie is complete without a crowd scene or two, but for animators they are a headache. Audiences are not fooled if one character is simply copied many times over; although individuals in a real crowd tend to act in similar ways, they retain their own idiosyncrasies. A new study has identified tricks that can prevent a clone sticking out like a sore thumb. Rachel McDonnell and colleagues at Trinity College Dublin, Ireland, studied two types of animated clones: appearance clones that are identical, and motion clones, which appear different but move in the same way. Unsurprisingly, they found that appearance clones were quickly detected. Volunteers presented with a group of 12 static characters, two of which were identical, needed on average just 5.7 seconds to spot the clones. Motion clones proved more difficult to spot. When shown a grid of 12 walking mannequin models, two of which shared the same walking style, volunteers took more than 60 seconds to identify the clones. McDonnell says that means animators could use just a few walking styles to generate a crowd scene with a low risk that the clones would be detected. The motion clones became even harder to spot if they were animated to walk out of step with each other – a more likely scenario in a crowd scene. Volunteer clone-spotters were shown crowds of 20 characters walking out of step, up to 10 of which were motion clones. Even when 50% of the crowd shared the same walking style, it still took volunteers around 10 seconds to spot an identical pair. Techniques to rapidly capture high-resolution 3D scans of people and then animate them (with video) are becoming cheaper, making appearance clones easier to avoid. Using McDonnell’s tips, many scans of different people moving with the same motion could be effectively hidden. Even appearance clones can be made harder to pick out. The researchers found they could almost double the detection time by choosing the relative positions of clones in a crowd. When diagonally from one another on screen, detection time jumped from around 5 to 10 seconds. “Appearance clones on the same vertical or horizontal plane were easily detected,” says McDonnell. “That could be important for reconstructing a stadium crowd – you’d make sure no clones lie side by side either vertically or horizontally.” The team’s results offer rules of thumb for animators to ensure their crowd scenes are realistic, even when time or budget constraints make clones inevitable. “We are the first to examine the perception of crowd variety and to attempt to quantify the contributing factors,
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